The present invention relates to an ultraviolet (xe2x80x9cUVxe2x80x9d)/blue light excitable, visible light emitting phosphor. It finds particular application in conjunction with light emitting devices comprising a UV/blue light emitting die used in conjunction with the UV/blue excitable, visible light emitting phosphor and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
The advent of UV and blue LEDs of GaN-based epitaxial structures allowed, for the first time, generating white light from an LED. Luminescent phosphor materials have, heretofore, been applied on top of the LED. The phosphor material partially transforms the UV/blue light into longer wavelength visible light.
As used herein, the term xe2x80x9cUV/blue LEDxe2x80x9d means an LED emitting in the UV range, or in the blue range, or in both the UV and blue ranges of the electromagnetic spectrum.
Successful implementation of such a device is of course dependent upon the efficient conversion of UV/blue light into visible light of the desired wavelength and the subsequent efficient extraction of the generated visible light from the device.
However, the medium of the UV die in such devices is relatively lossy and, therefore, the phosphors only partially absorb the light from the LED. The unabsorbed light is partially reflected by the phosphor particles back in the direction of the LED, and partially transmitted through the phosphor layer, in both cases reducing the total possible visible light output.
In addition, visible light emitted by the phosphor may never leave the device, due to internal reflection and/or absorption at various locations within the device structure.
The present invention provides a new and improved apparatus and method which overcomes the above-referenced problems and others.
A light emitting device includes a nitride compound, for providing at least one of blue and ultraviolet emission. An epoxy, embedded with a phosphor, is mounted to the nitride compound. A frame includes a surface having an uneven portion contacting the epoxy.
In accordance with one aspect of the invention, the nitride compound includes one of binary compound materials, ternary compound materials, and quaternary compound materials.
In accordance with a more limited aspect of the invention, the nitride compound is one of a group II through group VI-nitride compound.
In accordance with an even more limited aspect of the invention, the nitride compound is a group III-nitride including GaN.
In accordance with another aspect of the invention, the nitride compound and the epoxy are mounted to a substrate.
In accordance with a more limited aspect of the invention, the substrate includes sapphire.
In accordance with another aspect of the invention, the uneven portion is a designed surface.
In accordance with another aspect of the invention, the phosphor converts the at least one of the blue and the ultraviolet emission from the nitride compound to a visible light, which is emitted from the frame.
In accordance with another aspect of the invention, the frame further includes a smooth portion. Substantially none of the phosphor embedded epoxy contacts the smooth portion.
One advantage of the present invention is that it converts relatively more UV/blue light to visible light.
Another advantage of the present invention is that it efficiently converts UV/blue light, which is emitted toward the bottom of an LED die, to visible light.
Another advantage of the present invention is that the surface area of the lead frame, which contacts the phosphor, is created to increase the conversion of UV/blue light to visible light and concurrently decrease die epoxy degradation, which in turn increases system reliability.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.